This project is concerned with the developmental consequences of hypothyroid and hyperthyroid states which are experimentally induced in rhesus monkeys and rats around the time of birth and the more immediate effects of thyroid alterations in learning and motivation tasks administered to normal adult animals. Efforts will be continued to establish rhesus monkey models of human cretinism and congenital hyperthyroidism, with particular attention given to the nature and persistence of learning deficits. The adult-animal studies have the dual purpose of clarifying the potentially confounding effects of chronic motivational, metabolic, and hormonal factors in the assessment of learning capabilities in the perinatally-treated animals and of revealing disorders of cognitive and emotional functioning which are analogous to various forms of psychopathology observed in hyper- and hypothyroidism in human adults. The latter purpose will involve studying the behavioral effects of interactions between thyroid hormones and brain catecholamines.